Hemoglobin is best known as red blood cells' superstar protein—carrying oxygen and other gases on the erythrocytes as they zip throughout the bodies of nearly all vertebrates. Less well known is its presence in vegetables, including the sugar beet, in which Nélida Leiva-Eriksson recently discovered the protein while working on her doctoral thesis at Lund University in Sweden. In fact, many land plants—from barley to tomatoes—contain the protein, says Raúl Arredondo-Peter, an expert on the evolution of plant hemoglobins, or leghemoglobins, at the Autonomous University of the State of Morelos in Mexico. “Hemoglobins are very ancient proteins,” he notes. Scientists first discovered them in the bright-red nodules of soybean roots in 1939 but have yet to determine the proteins' role in plants in most cases. One popular idea is that hemoglobin binds with and delivers nitric oxide to cells, sending signals to regulate growth.
Researchers are now investigating ways to leverage leghemoglobins. For example, Robert Hill, a plant biologist at the University of Manitoba, found that genetically engineering alfalfa to produce more of the proteins boosted the crop's survival rate during a flood from 20 to 80 percent. Plant hemoglobins might even serve as a blood substitute for humans someday—an idea that Arredondo-Peter says is conceivable but far off because they do not carry and release oxygen at the same rates as human hemoglobins. Or they could be exploited to trick our senses: food scientists at Stanford University are experimenting with plant hemoglobins as an ingredient in veggie burgers to make them taste more like bloody steaks.